1. Field of the Invention
The present invention relates to a structure for earphones, and more particularly, to a structure for dual-frequency coaxial earphones.
2. Description of Related Art
Referring to FIG. 1, a cross-sectional view illustrating a conventional earphone, the earphone 9 comprises a case 90, a cord 91, a diaphragm 92, a permanent magnet 93, a voice coil 94, a pole piece 95, and a yoke 96.
As shown in FIG. 1, the cord 91, the diaphragm 92, the permanent magnet 93, the voice coil 94, the pole piece 95, and the yoke 96 are received in the case 90, respectively, wherein the voice coil 94 is disposed on the diaphragm 92 and surrounds the permanent magnet 93, while maintains a gap, radially, with the pole piece 95. The permanent magnet 93 is interposed between the pole piece 95 and the yoke 96.
The cord 91 is electrically connected with the voice coil 94, so that when acoustic frequency signal is transmitted to the voice coil 94 via the cord 91, the voice coil 94 produces a magnetic field due to a magnetic effect. The magnetic field will then magnectically interact with the pole piece 95, making the diaphragm 92 vibrated and the acoustic frequency signal converted into and outputting an acoustic frequency wave.
Conventionally, an acoustic frequency signal involves a high frequency speaker part and a low frequency speaker part. Therefore, vibration of a diaphragm produces, simultaneously, a high acoustic frequency wave and a low acoustic frequency wave. However, since the high and low frequency acoustic waves involve characteristics of different wavelengths and amplitudes, respectively, the diaphragm cannot distinguish clearly the characteristics from one another. As such, the conventional earphone results in a shortage of intermodulation of distortion for the high and low acoustic frequencies, and fails to produce a clear sound. To overcome the shortage, if a high frequency speaker and a low frequency speaker are arranged together in an earphone, a bulk size will make the earphone impractical.